Microwave transmission system



Aug. 8, 1950 R. L. sPRoULL MICROWAVE TRANSMISSION SYSTEM 2 Sheets-Sheet 2 Filed April 9, 1946 M 2 M R. H ..11 w m f M .m9 om. m* M T V nl N T l A AW n H AWN ,.m, y ,di I M M w Y B J 7, UA l.

Patented ug. 8, 1,950

MICROWAVE TRANSMISSION SYSTEM Robert L; Sproull, Ithaca, N. Y., assignor to Radio Corporation of America, a corporation of Dela- Application April 9, 1946, Serial No. 660,594

(Cl. Z50-17) 8 Claims.

1 This invention relates generally to microwave transmission systems and more particularly to improved methods of and means for switching a `microwave generator between a plurality of load circuits without the use of moving mechanical elements.

Various types of switching systems for microwave energy have been used heretofore which employ moving mechanical elements for selecting the desired one of a plurality of load circuits -for connection to a microwave generator. Such movable mechanical elements introduce erratic operation and transmission losses due to variations in contact potential and by inherent discontinuities in circuit conformation. The instant invention contemplates the use of a system of cavity resonators or resonant coaxial lines wherein the different load circuits are selectively coupled to predetermined different resonant modes of said resonators or lines, and wherein different ones of the modes are excited by varying the frequency of the microwave generator.

`In` a typical embodiment of the invention, a microwave generator of the reflex velocity modulation` type is coupled into a cavity resonator having a plurality of resonant modes which are excited by different microwave frequencies. Coupling apertures, or coupling loops extending into the cavity resonator, couple different load waveguides or lines to the resonator only when it is excited at a predetermined one of the resonant modes. Thus, one of the load lines is coupled to the resonator for one predetermined operating -frequency and another of the load lines is coupled to the resonator for a different operat- 1 ing frequency. Switching is accomplished by varying the operating potentials applied to the velocity modulation reex generator whereby the combined generator and cavity resonator is caused to oscillate at either one of the desired operating frequencies.

. Systems of this type may be employed as leftl right switching radar systems such as are employedfor directing gun re, aeronautical navigation or for various types of homing directional radio devices. A novel coupling circuit and double dipole directional antenna system also is disclosed for utilizing the invention for directional transmission purposes. i

Among the objects of the invention are to provide an improved method of and means for switching microwave energy. Another object is to provide an improved method of and means for switching a microwave generator between a plurality of microwave load circuits without the erator.

use of movable mechanical elements. A further object is to provide an improved microwave transmission system comprising an adjustablel frequency microwave generator coupled to a resonant device having a plurality of resonant modes, and a plurality of load circuits selectively coupled to different ones of the resonant modes. An

additional object is to provide an improved microwave switching device comprising an adjustable frequency microwave generator coupled to a cavity resonator having a plurality of resonant modes, and a plurality of waveguides connected to different load devices and coupled into said resonator to abstract microwave energy therefrom in response to excitation of different ones of said resonant modes.

A further object is to provide an improved microwave transmission system including a microwave generator coupled into a bi-resonant cavity resonator, a plurality of load circuits also:`

coupled into said resonator and responsive to excitation of different ones of said resonant modes, and means for varying the frequency of said` generator for selectively exciting different ones Vof said modes. videan improved directional microwave transmission system including an adjustable frequency microwave generator coupled to a resonant device having a plurality of resonant modes excited at different frequencies, and a pair of waveguide transmission systems terminated in directionalv antenna elements and coupled to said resonant circuit in different ones of said modes whereby said antennas are separately excited by prede" termined variation of the frequency of said `genexcited microwave antennas.

The invention will be further described by v reference to the accompanying drawings of which Figure 1 is a cross-sectional, partially plan view of a first embodiment of the invention; Figure 2 A is a cross-sectional, partially plan view of a modication of said rst embodiment of the invention`;' Figure 3 is a graph indicative of the multi-resonant operating characteristics of the invention;

Figure 4 is a cross-sectional, plan view of a second embodiment of the invention; Figure 5 is a Another object is to pro-r,

A further object is to provide a direc- Q tional antenna and coupling system therefor in- 't cluding a common reflector for said selectively j antenna and coupling system. Similar reference characters are applied to similar elements throughout the drawings.

Referring to Figure l, a typical microwave generator I of the reflex velocity modulation type includes a cathode heater element 3 for energizing an indirectlyheated thermionic cathoder, and an electron accelerator 1, for accelerating and directing the electron beam through an apertured axial portion 9 of a toroidal cavity resonator I I, and a reflector electrode I3 all disposed on a common axis within an evacuated envelope I5. The cathode may be grounded, the acceleration electrode may be'biased at a fixed positive potential from a source not shown, and the reflector electrode I3 may have impressed thereon a suitable negative potential to reflect the electron beam back through the central portion 9 of the cavity resonator I I. By connecting a source of control signals I'I to the reflector electrede- I3, the potential thereon Amay be varied Vin a; manner providing an effective control of the microwave frequency which is generated. The operation of such generators is well known in the'lart.

fA microwave-permeable, gas-tight window4 I9 in the side of the cavity resonator II of the microwave generator I lopens into a second cavity resonator 2l which is proportioned to resonate in the modes indicated by the solid and dash line arrows 2-3 and 25, respectively, indicating the nia'gnetic field. By varying the potential applied to the reflector electrode I3l in response to control signals from the sourcev I'I, the output frequency generated by the reflex' oscillator will Vdepend upon the resonant characteristics f the combined system` including the tube cavity resonator Hand the second cavity resonator 2|. Thus, the. generated frequency will depend upon the mode of excitation lof the secondl cavity resonator 2|, and the control signal sourc'eor control voltage applied to the reflector electrodev I3` will cause the combined system to generate'oscillations which may shift from one predetermined frequency to a second predeterminedfrequency as different modes of the second cavity resonator areexcited.

[A first waveguide 2l, which may be connected,

toa' lfirst load, not shown, is coupledA into the secondcavity resonator 2l by means of a couplingV aperture 29 in a manner whereby microwave 'en" ergy'is abstracted from the cavity resonatorgand applied to the load only when the resonator is" excited in the mode indicated by the solid line arrows 23. When the system is resonatingin this. "mode, the resultant coupling through ra second coupling aperture 3| to a secondwaveguide 33 connected to a second load, not shown,

is effectively zero, since the second aperture 3| is located at a null point between the magnetic fields of the resonant mode 23. second' cavity resonator l2| is. excited in the mode indicated by the dash line 25,'eifective microwave coupling is provided through the second aperture 3l and second waveguide33 to the second load instead of through the rst aperture 29 and .the rst waveguide 22 ,to the first load.

.It should'be understood that the coupling aperture I9 between the ca-vity resonator II and 2I, should be quite large" in order to provide close coupling therebetween. The reflex generator I has ybeen illustrated Vin elevation as'compared to'V the plan View of` 'the' cavity' resonator 2l and waveguides 21 and 2'3, in order' to illustrate more completely the structural details of such a system.'

However, if the 4 It should be understood, however, in Figs. 1, 2 and 5, that the portion of the structure to the left of the axis 35 should be rotated 90 with respect to the structure illustrated to the right of said axis.

The system shown in Figure 2 is a modification of that described heretofore by reference to Figure l wherein-the structure is modified only in a manner whereby two-cell and three-cell .resonant modes indicated by the dash lines 25 and 23, respectively, are excited within the cavity resonator EI. This arrangement permits switching between two operating frequencies which are much more closely related than is possible with "the two-cell resonator shown in Fig. l.

The first coupling aperture 29 couples the first load through the first waveguide 2l to the cavity resonator 2i only when it is excited in the mode 25 shown in dash lines. Also the second coupling aperture 3l couples thesecond load through the second waveguide 33 to the cavityv resonator 2I only when it is excited in theY mode shown by the solid lines 23. This type of modal excitation ofthe cavity resonator provides practically complete cut-olf'of energy through one of 'the waveguides when the other abstracts energy for its associated load, since the modes are so positioned that the resultant magneticcoupling is maximum through one aperture and practially negligible through the other, no matter which' mode is excited.

The graph of Figure 3 indicates the-power output which may be derived from thev cavity resonator 2l and applied to the rst and second loads, respectively, as the frequency is' varied between the values f1 and fz' by varying the reflector con-Y trol voltage VR between the values-V1 and V2; The additional power peaks 3l, 39,'41 and 43 indicate other less efficientpairs of modes which may loe-utilized if desired.

Figure 4 shows a second embodiment of the invention vwherein a conventional magnetron generator 5i of the variable frequency type is coupled through a coaxial transmission line 53 to a'resonator 55 having perpendicularly disposed resonant modes indicated by the solid and dash line arrows5'I, l59, respectively, A system utiliz* ing such a resonator may be operated for switching kbetween two closely related frequencies determined by the relative lengths of the transverse" axes Bland 63 Aof the resonator.

' A first load, not shown, is coupled to the resonator through a first load transmission line 65 which is terminated in a coupling loop 61 disposed upon the horizontal transverse resonator' axis 63. This load is coupled to the generator only when the resonator 55 is excited in themode indicated by the dash linel arrows 59. Similarly a second load is coupledrto the resonator' through a second coaxial load line 59 terminated in' a.' second coupling loop ll disposedon the verticalv transverse resonator axis 6I, whereby energy is coupledv to theVv second load only when the resonatorit is excited in the mode' indicated'by the solid line arrows 6l'. Substantially perfect cancellation of energy transfer is provided foreach load circuit when the other' load circuit is abstr'acting energy from the resonator'. .It should?V of in Fig. 4 has been employed to clarify and.' simplify the structural relations between ele-*' ments.'

Referring to Figures 5 and 6, any of the systems described heretofore may be employed to actuate a selectively directional antenna system for providing angularly disposed radiation lobes and Tl in response to selective excitation of dipoles 'I9 and Si which are, respectively, disposed at .points within the curvature of and eccentric `tothe axis of a parabolic wave reiiectcr 83. The lengths of the waveguides 21 and 33 coupling the `dipoles to the cavity resonator 2l may be so 4proportioned that an effectively innite impedance lis presented to the undesired frequency .when energy of said frequency is propagated through the other of said waveguides. Suchpro- `j )ortioning` of the waveguides is highly desirable since otherwise 'they might parasitically absorb considerable energy from the undesired resonant mode in the resonator 2i.

Figure 6 illustrates in greater detail a satisfactory arrangement of the bi-directional double dipole antenna system forming a portion of the system of Fig. 5, the operation of which has been described heretofore.

Thus, the invention described comprises an improved method of and means for switching a microwave generator between a plurality of load circuits without the use of moving mechanical elements, wherein a cavity resonator or other resonant device may be selectively excited in two different resonant modes by shifting the generator frequency, and wherein different load circuits are selectively and substantially exclusively coupled to said resonator in only one of its modes of excitation. The system further has been described in combination with a bi-directional antenna system of the type employed in directional navigation systems and the like.

I claim as my invention:

l. An ultra-high frequency energy switching system for selectively connecting a source of energy to different load elements, said system including a cavity resonator coupled to said source and having at least two different longitudinal resonant modes, means for coupling one of said load elements to said resonator to extract energy in one of said modes, means for coupling another of said load elements to said resonator to extract energy in another of said modes, and means for varying the frequency of said energy source to excite said resonator selectively in diierent ones of said modes.

2. An ultra-high frequency energy switching system for selectively connecting a source of en ergy to different load elements, said system including a cavity resonator coupled to said source and having atleast two different parallel resonant modes, means for coupling one of said load elements to said resonator to extract energy in one of said modes, means for coupling another of said load elements to said resonator to extract energy in another of said modes, and means for varying the frequency of said energy source to excite said resonator selectively in different ones of said modes.

3. An ultra-high frequency energy switching system for selectively connecting a source of energy to diierent load elements, said system including a cavity resonator coupled to said source -allel resonant modes, means for coupling said source to said resonator through one of said apertures, a rst waveguide opening into said resonatorcthrough one of said apertures for'coupling one of said load elements to said resonator to extract `energy in one of said modes, a second waveguide opening into said resonator through another of said apertures for coupling another of said load elements to said resonator to extract energy in another of said modes, and means for varying the frequency oi said energy source to excite said resonator selectively in different ones of said modes.

5. An ultra-high frequency energy switching system for selectively connecting a source of energy to diiferent load elements, said system including a first cavity resonator having a plurality of coupling apertures and at least two diiferent parallel resonant modes, said source including a second cavity resonator opening into said first resonator, a first waveguide opening into said rst resonator through one of said apertures for coupling one of said load elements to said resonator to extract energy in one of said modes, a second waveguide opening into said first resonator through another of said apertures for coupling another of said load elements to said resonator to extract energy in another of said modes, and means for varying the frequency of said energy source to excite said first resonator selectively in diiferent ones of said modes.

6. An ultra-high frequency energy switching system for selectively connecting a source of energy to different load elements, said system including a cavity resonator having a plurality of coupling apertures and at least two different parallel resonant modes, said source comprising a reflex microwave oscillator having a frequency controlling electron reflecting electrode and a second cavity resonator opening into said first resonator, a first waveguide opening into said rst resonator through one of said apertures for coupling one of said load elements to said resonator to extract energy in one of said modes, a second waveguide opening into said first resonator through another of said apertures for coupling another of said load elements to said resonator to extract energy in another of said modes, a source of potential for said electrode and means for varying said potential for varying the frequency of said energy source to excite said resonator selectively in different ones of said modes.

7. An ultra-high frequency energy switching system for selectively connecting a source of energy to different antenna elements, said system including a cavity resonator having a plurality of coupling apertures and at least two diiferent parallel resonant modes, means for coupling said source to said resonator through one of said apertures, a first waveguide opening into said resonator through one of said apertures for coupling one of said antenna elements to said resonator to extract energy in one of said modes, a

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second waveguide opening into 'said `resonator through another fof said apertures vfor coupling another of said `antenna elements to said ,reso- -nator v.to .extract energy in another of said modes,

and Ameans for varying the yfrequency of said energy vsource to excite said resonator selectively .in different ones of said modes.

8.' `A system according to claim '7 including a parabolic wave reflector having said antenna vele- ;ments positioned eccentrca'lly with respect to its axis, 'there'la'tve .lengths of said waveguides 'being proportioned to .minimize parasitic wave propagation therein in .response to wave transmission through the other of said waveguides, whereby vexcitation of said resonator .in Adifferent ones of .its resonant modes VYprovides selective variation 'of the direction of wave propagation from Isaid reflector.

ROBERT L. -SPROULL REFERENCES CITED The following `references 'are of record .in lthe 'le of this patent:

UNTIED STATES PATENTS Number Name Date f "2,054,816 Hollmann Sept. 22, 1936 2,067,156 yLux Jan. 5, 1937 '2,337,184 :Carter Dec. 21, 1943 '2,380,981 McElhannon Aug. 7, 19'45 2,408,425 Jenks et a1 Oct. v1, 1946 A2,409,227 vSho'clley Oct. 15, '19'4'6` 2,421,725 Stewart June 3, '-1947 '2,425,328 Jenks et al Aug. 12, 194'? '2,444,152 Carter June 29, 1948 '2,450,026 Tomlin Sept. 28, 1948 

